An experimental, direct injection (DI), alcohol-fueled, engine combustion system has been developed for application to diesel engines used in medium duty trucks. A single cylinder version of a 6.6L, 6-cylinder DI diesel engine was designed, built and tested. The baseline diesel engine had a helical port with a moderate swirl ratio of 2.74, a 16.3:1 compression ratio, and a multi-spray fuel injection system. The engine was converted to operate on ethanol and methanol fuels with provisions for spark or glow plug ignition assist. Compression ratio was increased to 19.3:1. A higher rate inline fuel injection pump and larger hole area nozzles were installed to accommodate the larger fuel volume flow rates with alcohol fuels. An experimental high energy, multi-strike ignition system was used to directly ignite one of four fuel-spray plumes. Combustion initiated from the first plume ignited the remaining three plumes via a proposed process of flame propagation from the initial ignition site followed by compression ignition of the peripheral regions of the plumes not yet in contact with the flame. Parametric studies were conducted to optimize ignition and injection system variables, and to examine the effect of increasing combustion chamber temperature levels via heated inlet air. The DI alcohol engine produced a 9 to 15% increase in full load BMEP, and a 1 to 1.5% reduction in energy consumption based on the EPA 13-mode transient cycle relative to the baseline DI diesel engine.